Summary of Work: This projects utilizes peripheral blood obtained from participants in the Baltimore Longitudinal Study of Aging (BLSA) to gain insight into the biological, biochemical, and molecular mechanisms underlying age-associated changes in human immune function. A number of studies have suggested that human T lymphocytes obtained from aged individuals exhibit an altered immune response to various immunological vaccines and polyclonal stimuli both in vivo and in vitro. In comparison with immune cells obtained from younger individuals, aged leukocytes also display distinctive patterns of protein phosphorylation, cytokine synthesis and gene expression, and cell-cycle progression.